Cholera toxin in vitro catalyses the transfer of ADP-ribose from NAD ion to a number of cellular proteins. These are a) 42K, somtimes 50K, which are regulatory components of adenylate cyclase, b) often 98K, 23K, which share sequences with 42K but whose nature isn't clear, c) even more minor components that have not been studied at all. In the coming year we shall continue to study the minor components, especially 98K, to determine its physiological function and the possible change of function upon ADP-ribosylation. We shall use erythrocytes and enterocytes. We shall also examine non-vertebrate tissues to see what targets, if any, they have, what their sizes are, when they arose, or changed size, and how these changes relate to the evolution of adenylate cyclase and its regulatory systems.